Method of sparging fluids into rolling beds of particulate solids



-' May 27, 1969 w. A. M PHERSQN ET AL 3,446,486 METHOD OF SPARGINGFLUIDS INTO ROLLING BEDS OF PARTICULATE SOLIDS Filed Jan. 26, 1967INVENTORS Wilbur A. Mc Pherson Robert w. Hamilton Coil A. Cline AGENTUnited States Patent US. Cl. 259-15 1 Claim ABSTRACT OF THE DISCLOSUREFluid is sparged into a highly turbulent zone of a rolling bed ofparticulate solids in a horizontal revolving drum with minimum drag onthe bed by permitting forces acting in the bed to move the sparger in asubstantially vertical path, intersecting at a substantial angle thenodal area between particles which are being lifted upward and thosewhich are flowing downward.

SUMMARY OF INVENTION In the manufacture of fertilizer it is commonpractice to employ a horizontal revolving drum apparatus for the mixing,agglomerating and carrying out reactions of fluids with particulatesolids. The drum is usually arranged in a substantially horizontalposition, slightly inclined, and is revolved by means of an externaldrive through a ring gear which surrounds the periphery of the drum.Considerable power is consumed in revolving a drum containing a bed ofparticulate solids. This is easily demonstrated by filling an oil drumapproximately one-third full of moist sand, laying it on its side, androlling it. It will be found to require considerable work to roll a drumpartly filled with moist sand, whereas a drum completely filled withsand rolls quite easily on a level surface. The reason is, of course,that a partly filled drum must continuously lift a mass of particulatesolids centered below the axis in order to turn, whereas in the filleddrum the mass is centered along the axis and is not lifted. The solidswhich are lifted consume the power, and the energy absorbed by liftingis then dissipated as the particles roll downward from the top of thebed. With all of the energy expended in rotating the drum going into therolling bed of particles, it is apparent that the bed is capable ofexpanding this energy intermittently by exerting rather large forcesover a substantial distance. In carrying out reactions in a rolling bed,as for example in ammoniation of particles of calcium superphosphate, itis a preferred practice to submerge a perforated .pipe or other form ofsparger by means of a strong supporting structure within the bed in aturbulent zone, usually as near as possible to a nodal area separatingthe particles which are moving upward from those which are flowingdownward. This type of arrangement is illustrated, for example, in U.S.Patents 2,741,545 and 2,945,747. In spite of the most carefulpositioning of the sparger, it is found that considerable force isexerted against the sparger and its mountings from time to time and veryoften a sparger is suddenly broken or wrenched loose from its mountingswithout previous indication of potential trouble. The forces exertedagainst the sparger result from variations in the flow paths of theparticles. This may be occasioned by the clumping of some particlestogether or by variations in the amount of liquid in the bed atdifferent places. Or, as often happens, the amount of force on thesparger continuously increases because of the formation of soliddeposits upon the sparger itself. It is a common practice to reverse thedirection of rotation of the drum for short periods of time in order tobreak off the solid deposits clinging to the sparger pipe.

It has now been discovered that the drag of the sparger against themoving bed can be reduced to a minimum by mounting the sparger in Such away that it moves in response to forces exerted by the particles in thebed in a substantially vertical path, which intersects at a substantialangle the model area between particles which are moving upward andparticles which are flowing downward. In both FIGURE 1 and FIGURE 2 ofthe drawing are illustrated mountings of a sparger pipe so that it movesthrough a vertical path CD which intersects the nodal surface AB whichseparates upward flowing particles from downward flowing particles. Bypermitting the sparger pipe to be moved up or down by the forces exertedwithin the bed, there is a tendency for the upward and downward forcesexerted against the sparger to be balanced out so that the spargerremains at all times substantially in the nodal surface, moving up anddown with variations in the flow pattern of particles. The followingexamples are presented for illustrative purposes.

Example] In a pilot plant size granulating drum having a diameter ofabout four feet was placed a quantity of superphospate which wasmoistened with phosphoric acid and was continuously ammoniated by meansof a sparger made of perforated on-quarter inch pipe mountedlongitudinally on two arms, one attached at each end in the manner shownin the diagram of FIGURE 1. The moving bed of solids was about fourinches deep. Ammonia Was fed through the perforated sparged pipe whilethe drum was rotated at a peripheral velocity of about feet per minute.The arm was observed to move up and down over a very short path ratherslowly and unevenly without exerting substantial force on the support onwhich the arms were pivoted. When ammoniation was begun and thetemperature and moisture content in the bed began to change, it wasnoticed that the sparger appeared to change its position in the bed,indicating that the forces being exerted from opposite sides of thesparger pipe had undergone a change. From this it was concluded that ifthe sparger had been placed in a fixed position, the substantial changesin moisture content in the bed would have caused an increase in the dragof the sparger. Continuous operation over a period of about six hourssuccessfully demonstrated that the method of sparging resulted inminimizing forces exerted against the sparger pipe as well as formationof solid deposits on the pipe. The apparatus was shut down and startedup the following day without problems, was operated again for six hours,and this was again repeated on the next day without difiiculty in eitherstart-up or continuous operation.

Example II In: a fertilizer manufacturing process, a horizontal rotatingdrum is employed, which is approximately fortyfive feet in length, tenfeet in diameter and has a horizontal slope of about 17 inches from thefeed end to the discharge end. In this drum, approximately one ton ofparticulate solids are treated at one time. In tammoniation ofsnperphosphate, a perforated sparger pipe distributes liquid ammoniafrom a supply tank into the bed of solids. The sparger pipe is mountedwith a four-bar arrangement at each end as illustrated in FIGURE 2 ofthe drawing. The four-bar mounting is made of corrosion-resistantmaterials. With the minimizing of forces exerted against the mounting,the parts need not be of heavy construction.

The four-bar linkage for obtaining desired types of motion is well knownto mechanical engineers. (See for example C. M. Ham et al., Mechanics ofMachinery, fourth edition, pages 19 to 22, McGraw-Hill, 1958.)Preferably the movable ar ms, customarily called the crank, rocker andconnecting rod, may be adjusted in length with respect to each other inorder to obtain a path CD, as shown in the drawing, which has thedesired shape. As the volume of the bed of particulate solids, theirspecific gravity, moisture content and so forth are varied, the nodalarea AB separating upward moving from downward moving particles willchange in curvature and position and the forces exerted by movingparticles will change in magnitude. It is therefore desirable to be ableto make adjustments in the positions of pivots so as to obtain the typeof path of sparger movement which will minimize oscillations of spargerand substantially eliminate drag. This may be conveniently accomplishedby using support arms which contain a number of holes, so that pivotbolts can be changed in their positions. This type of mounting for thesparger is very economical with respect to space, leaving considerableroom at the lower portion of the rolling bed of particulate solids. Itmay be desirable to have this area clear of obstructions for the purposeof reactor cleaning or addition of liquids to the top of the moving bedwith a spray arrangement.

It happens occasionally that a solid deposit forms on the inside wall ofa granulating drum and breaks loose, falling on the bed. Large chunks ofsolids which get into the moving bed in this way are often responsiblefor damage to submerged spargers. The apparatus shown in FIGURE 2 isfound to move very quickly in response to forces exerted by large chunksof material in the bed, relbcating the sparger after the chunks havepassed by, with no damage to the apparatus. This apparatus may also beused conveniently in a drum equipped with flights attached to the wall,the sparger being lifted out of the way as each flight passes under itand immediately repositioning itself thereafter.

It is necessary for the vertical path of sparger movement to intersectthe nodal area represented by crosssection AB at a substantial angle inorder to prevent violent sparger movement. When the path of spargermovement almost coincides with the contour of the nodal area there is atendency for the sparger to be alternately lifted and swept backdownward so that it oscillates rapidly, resulting in loosening ofmounting bolts, excessive wear and eventual fatigue of the sparger pipeor its supports. The existence of vibration with resulting fatigue ofmetal parts is believed to be a cause of mechanical failures experiencedwith fixed spargers, in spite of efforts to mount them as rigidly aspossible.

It will be understood that the limiting of the movement of the spargerpipe to a substantially vertical path may be readily accomplished byother mechanical arrangements. Whatever arrangement is used, however, itshould be kept in mind that the supports for the sparger should offer aslittle resistance to flow of solids as possible, so that the forceswhich are exerted against the sparger by the moving particles areexerted primarily against the sparger pipe itself. In view of the factthat the method of sparging results in a cancellation of forces, thesupport structure may be quite thin in cross-section and light inweight. In operation it is found that the sparger moves up and downirregularly, indicating that it is adjusting itself to a changingbalance of forces and these variations are believed to account for thelack of large deposits of solids on the sparger pipe. It appears thatthe irregular variation of forces in the bed and in the position of thesparger exert a scrubbing action which keeps the sparger pipesubstantially free of solid deposits which would otherwise exert drag onthe bed. Furthermore, since the sparger does not press against the bedas fixed spargers do, deposits do not tend to accumulate on the interiorwall of the rotating drum.

What is claimed is:

1. A method of sparking a fluid into a rolling bed of particulate solidscomprising sparking fluid through open.- ings in a conduit for saidfluid which is flexibly mounted so that the conduit is permitted to moveonly in a substantially vertical path in response to forces exerted bythe :moving particles in the bed, said vertical path intersecting at asubstantial angle the nodal area between particles being lifted upwardand particles which are flowing downward.

References Cited UNITED STATES PATENTS 2,122,551 7/1938 Allingham 259-142,741,545 4/1956 Nielsson 23259.1 2,945,747 7/1960 Nielsso-n 23-25912,946,666 7/1960 Eymann 23-259.l

ROBERT W. JENKINS, Primary Examiner.

